This invention relates generally to combustion of gaseous fuels wherein the NOX content in products of combustion or flue gases are reduced to acceptable levels. More particularly, this invention relates to low NOX combustion systems fired by fluid fuels, including oil, and other hydrocarbons such as alcohol and toluol in compact boilers and similarly constructed fluid heaters.
In the above-mentioned copending application, a system of controlling flue gas NOX content through controlling the ratios of injected flue gas, steam and ambient air, into the primary and secondary combustion air, and directly into the combustor. In that application the flue gas is scavenged or intercepted in the boiler exhaust.
Although the system disclosed in the above-mentioned co-pending application is creditable, applicants, in continuing investigation and product development, have discovered additional methods for reducing NOX, particularly in the "compact" boiler designs utilizing liquid fuels. The invention disclosed herein provides a method for reducing NOX in boiler stack emissions that is less complex, and equally effective in firing fluid fuels, including liquids.
Therefore, it is an object of this invention to provide a method and apparatus for reducing the NOX level in the stack emission of a compact boiler utilizing fluid fuels.
It is an additional object of this invention to provide a method and apparatus for reducing compact boiler NOX levels in stack emissions through controlling flue gas and/or steam injection into the primary and secondary air inputs to the boiler or heater.
It is another object of this invention to reduce the NOX content of compact boiler emissions through control of mixed tertiary air, flue gas and/or steam injection into the boiler combustion chamber.
It is a further object of the invention to provide sources of steam for NOX reduction from various components of the boiler configuration.